Heterotetranuclear M2(do)M′2(d8)(M = Ti or Zr, M′= Rh or Ir) complexes containing pyridine-3,5-dicarboxylate as an assembling ligand. Crystal structure of [(η5-C5H5)2Ti{µ-3,5-C5H3N(CO2)2}2Ti(η5-C5H5)2]

Abstract

Reaction of [M(η⁵-C₅H₅)₂Cl₂](M = Ti, 1a or Zr, 1b) in tetrahydrofuran (thf) with pyridine-3,5-dicarboxylic acid, in the presence of NEt₃, gives the homobinuclear species [(η⁵-C₅H₅)₂M{µ-3,5-C₅H₃N(CO₂)₂}₂M(η⁵-C₅H₅)₂](M = Ti, 2a or Zr, 2b) in good yields. The crystal structure of the titanium derivative 2a has been determined by X-ray analysis. The compound crystallizes in the monoclinic space group P2₁/c, with a= 12.666(4), b= 7.914(3), c= 16.443(7)Å, β= 108.21(3)° and Z= 2; R= 0.053 and R′= 0.086. The molecule consists of two (η⁵-C₅H₅)₂ Ti units linked by two pyridine-3,5-dicarboxylato ligands. Only one oxygen atom of each carboxylato group is involved in bonding to the titanium atoms, giving a 16-membered ring. The two pyridine rings are almost coplanar and adopt an orientation with the nitrogen atoms at the exterior of the ring. The geometry around the titanium atoms is nearly tetrahedral. Complexes 2a and 2b contain unco-ordinated pyridine nitrogen atoms which have been utilised in the synthesis of heterotetranuclear complexes. Reaction of 2a or 2b with [{Rh(CO)₂Cl}₂] or [lr(CO)₂(p-MeC₆H₄NH₂)Cl] in dichloromethane gives complexes [(η⁵-C₅H₅)₂ M{µ-3,5-C₅H₃N(CO₂)₂ M′(CO)₂Cl}₂M(η⁵-C₅H₅)₂](M = Ti, M′= Rh, 3a; M = Zr, M′= Rh, 3b; M = Ti, M′= lr, 4a; M = Zr, M′= lr, 4b) in near quantitative yields. Spectroscopic data support a structure in which the M′(CO)₂Cl moieties are bonded to the pyridine nitrogen atoms in complexes 2a and 2b. These are the first reported examples of complexes containing pyridine-3,5-dicarboxylate as an assembling ligand.